Update on Swine Influenza

While not strictly a "medicine for the outdoors" topic, swine influenza is a hot topic today. I've received more than a few communications from friends and family who are concerned about the significance of the emergence of this strain of influenza.

In the U.S., there are confirmed and probable cases of the new strain of H1N1 swine influenza that have been discovered in California, Kansas, and New York. It is important to note that many reports of cases have not yet been independently verified by public health officials or diagnostic testing. Thus far, the cases appear to be clinically mild. There will hopefully be more information soon about which cases are verified, and the severity of the infection in humans.

In Mexico, the media are also reporting additional possible cases in the last 24 hours, but these have not yet been confirmed by Mexican, U.S., or World Health Organization (WHO) authorities. President Felipe Calderón published an order today that would give his government powers to address a deadly flu epidemic, including isolation of persons affected by the rare virus, inspection of their homes, and mandated closure of any public events that might result in more infection.

The U.S. Centers for Disease Control reports that it is working closely with state and local officials in California and Texas, as well as with health officials in Mexico and Canada, and the WHO. The WHO held an expert meeting today to discuss the possibility of raising the pandemic alert level from its current level 3, but decided not to adjust that level.

Pandemic alert phases are outlined in the WHO’s 2005 global influenza preparedness plan, which makes recommendations for international and national measures to be taken during phases 1 to 6 of pandemic alert. The phases scale up or down according to the WHO’s assessment of the public health risk of a pandemic at that time.

According to the WHO’s global influenza preparedness plan, the decision to move between phases 3, 4, and 5 is based on “an assessment of the risk of a pandemic,” which may include consideration of “rate of transmission, geographical location and spread, severity of illness, presence of genes from human strains (if derived from an animal strain), and/or other scientific parameters.”

Below is a brief overview of the WHO’s pandemic alert levels relevant to this situation:

Phase 3 (current phase) of the pandemic alert period is when there are human infections with a new sub-type of influenza virus, but there is no human-to-human spread (or at least very rare instances of spread to a close contact). During Phase 3, the new virus subtype must be characterized rapidly to ensure early detection, notification and response.

Phase 4 occurs when there are small clusters (e.g., less than 25 human cases lasting less than 2 weeks) with limited human-to-human transmission. Spread is highly localized, which suggests the virus does not adapt well to humans. During this phase, WHO describes a variety of measures, such as targeted use of antiviral medications, aimed at containing the virus within a limited area or to delay virus spread to buy time to implement preparedness measures, such as vaccine development.

Phase 5 occurs when there are large clusters (e.g., 25 to 50 cases lasting 2 to 4 weeks), but human-to-human spread is still localized. The virus may not yet be fully transmissible. At this point, it is imperative to continue efforts to contain or delay spread of the virus, to both avert a pandemic and to implement pandemic response measures.

Phase 6 is when transmission to the general population has increased and is sustained, meaning there is a pandemic. All efforts to minimize the impacts of the pandemic are necessary at this time.

This current outbreak may be in its infancy or have been present for weeks - we just don't know. I am confident that highly skilled and motivated medical epidemiologists and clinicians are chasing the data as quickly as possible in order to effectively treat persons stricken with influenza and to avoid spread of the virus.

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